[Webkit-unassigned] [Bug 42061] Make base64Decode ignore unrecognizable characters

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=42061





--- Comment #6 from Kwang Yul Seo <kwangyul.seo at gmail.com>  2010-07-12 22:04:17 PST ---
(In reply to comment #5)
> (From update of attachment 61199 [details])
> Do we want this behavior for all callers of the function? RFC 2045 is specifically for the Base64 Content-Transfer-Encoding in MIME, not specifically for data URLs or for the window.atob function.

RFC3548 states:

2.3.  Interpretation of non-alphabet characters in encoded data

   Base encodings use a specific, reduced, alphabet to encode binary
   data.  Non alphabet characters could exist within base encoded data,
   caused by data corruption or by design.  Non alphabet characters may
   be exploited as a "covert channel", where non-protocol data can be
   sent for nefarious purposes.  Non alphabet characters might also be
   sent in order to exploit implementation errors leading to, e.g.,
   buffer overflow attacks.

   Implementations MUST reject the encoding if it contains characters
   outside the base alphabet when interpreting base encoded data, unless
   the specification referring to this document explicitly states
   otherwise.  Such specifications may, as MIME does, instead state that
   characters outside the base encoding alphabet should simply be
   ignored when interpreting data ("be liberal in what you accept").
   Note that this means that any CRLF constitute "non alphabet
   characters" and are ignored.  Furthermore, such specifications may
   consider the pad character, "=", as not part of the base alphabet
   until the end of the string.  If more than the allowed number of pad
   characters are found at the end of the string, e.g., a base 64 string
   terminated with "===", the excess pad characters could be ignored.


According to the specification, we must not ignore unexpected characters in general case.

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